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OCR for page 397
PART III: SULFATE 397 SULFATE ne of sulfate’s key roles in the body is in the synthesis of 3¢- O phosphoadenosine-5¢-phosphosulfate (PAPS), also known as active sulfate. In the body, active sulfate is used in the synthesis of many essential compounds, some of which are not absorbed intact when consumed in foods. Sulfate requirements are met when intakes include recommended levels of sulfur amino acids. Therefore, neither an Estimated Average Requirement (EAR), and thus a Recommended Dietary Allowance (RDA), nor an Adequate Intake (AI) has been established for sulfate. Overall, there were insufficient data to set a Tolerable Upper Intake Level (UL) for sulfate. About 19 percent of total sulfate intake comes from inorganic sulfate in foods and another 17 percent comes from inorganic sulfate in drinking water and beverages. Foods found to be high in sulfate include dried fruits, certain commercial breads, soya flour, and sausages. Beverages found to be high in sulfate include select juices, beers, wines, and ciders. Sulfate is also present in many other sulfur-containing compounds in foods, providing the remaining approximately 64 percent of total sulfate available for bodily needs. Sulfate deficiency is not found in people who consume normal protein intakes containing adequate sulfur amino acids. Adverse effects have been noted in individuals whose drinking water source contains high levels of inorganic sulfate. Osmotic diarrhea that results from unabsorbed sulfate has been de- scribed and may be of particular concern in infants who consume fluids de- rived from water sources with high levels of sulfate. SULFATE AND THE BODY Function Sulfate (inorganic sulfate [SO42–]) is required by the body for the biosynthesis of 3¢-phosphoadenosine-5¢-phosphosulfate (PAPS), also known as active sulfate. PAPS is used in the biosynthesis of chondroitin sulfate, cerebroside sulfate, and many other important sulfur-containing compounds, some of which are not absorbed intact when consumed in foods.

OCR for page 397
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 398 Absorption, Metabolism, Storage, and Excretion Sulfate can be absorbed in the stomach, small intestine, and colon. Absorption is a sodium-dependent active process. When sulfate is consumed in the form of soluble sulfate salts, such as potassium sulfate or sodium sulfate, more than 80 percent is absorbed. When sulfate is consumed as insoluble salts, such as barium sulfate, almost no absorption occurs. Unabsorbed sulfate is excreted in the fe- ces, reabsorbed in the colon, or reduced by anaerobic bacteria to metabolites. The primary route of excretion is through the urine. In addition to dietary sulfate intake from food and water, sulfate is derived in the body from methionine and cysteine found in dietary protein and the cysteine component of glutathione. In fact, most body sulfate is produced from the amino acids methionine and cysteine, both of which contain sulfur and are obtained from dietary protein and body protein turnover. DETERMINING DRIS Determining Requirements Dietary inorganic sulfate in food and water, together with sulfate derived from methionine and cysteine found in dietary protein, as well as the cysteine com- ponent of glutathione, provide sulfate for use in PAPS biosynthesis. Sulfate re- quirements are thus met when intakes include recommended levels of sulfur amino acids. For this reason, neither an EAR, and thus an RDA, nor an AI for sulfate has been established. The UL The Tolerable Upper Intake Level (UL) is the highest level of daily nutrient intake that is likely to pose no risk of adverse effects for almost all people. Overall, there was insufficient information available to set a UL for sulfate. Because there is no information from national surveys on sulfate intakes or on supplement usage, the risk of adverse effects within the United States or Canada cannot be characterized. DIETARY SOURCES Foods and Water About 19 percent of total sulfate intake comes from inorganic sulfate in foods and another 17 percent comes from inorganic sulfate in drinking water and beverages. The remaining approximately 64 percent comes from organic com-

OCR for page 397
PART III: SULFATE 399 pounds such as methionine, cysteine, glutathione, and taurine. Foods found to be high in inorganic sulfate include dried fruits, certain commercial breads, soya flour, and sausages. Beverages found to be high in sulfate include select juices, beers, wines, and ciders. An analysis of the sulfate content of various diets using foods purchased at supermarkets suggested a large variation in daily inorganic sulfate intake, ranging from 0.2–1.5 g (2.1–15.8 mmol)/day. The sulfate content of drinking water highly varies depending on where in the country it was obtained. Distilled water contains very little, if any, sul- fate, and deionized water contains no sulfate. However, an intake of inorganic sulfate as high as 1.3 g/day can be obtained from water and other beverages (0.5 g/L ¥ 2.6 L/day). Dietary Supplements Some people self-prescribe sulfur-containing compounds such as chondroitin sulfate, glucosamine sulfate, and methylsulfonylmethane as possible aids to bones and joints. Evidence has been presented suggesting that the beneficial effects of glucosamine sulfate for osteoarthritis may be due more to the sulfate than to the glucosamine contained in the compound. No data were available on the intake of sulfur-containing compounds. Bioavailability This information was not provided at the time the DRI values for this nutrient were set. Dietary Interactions This information was not provided at the time the DRI values for this nutrient were set. INADEQUATE INTAKE AND DEFICIENCY Unlike most other nutrients, the body’s need for sulfate can be met by con- suming other required nutrients that contain sulfur amino acids. Thus, a defi- ciency of sulfate is not found in people who consume normal protein intakes containing adequate sulfur amino acids. Ingestion of methionine, cysteine, and glutathione in foods, along with consumption of other sulfated compounds in both food and beverages, is sufficient to meet the body’s requirement for sulfate. Research with animals has shown that growth is stunted when dietary sul- fate is removed from the food and water supply, and when sulfur amino acids,

OCR for page 397
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 400 particularly cysteine, are provided at levels that result in deficiency signs. Rein- troducing sulfate to the diet prompts growth to resume. EXCESS INTAKE Adverse effects have been noted in individuals whose drinking-water source contains high levels of inorganic sulfate. Osmotic diarrhea resulting from unab- sorbed sulfate has been reported and may be of particular concern in infants who consume fluids that are derived from water sources with high levels of sulfate. Sulfate and undigested sulfur compounds have been implicated in the etiology of ulcerative colitis. High levels of hydrogen sulfide, produced in the colon from sulfate by sulfate-reducing bacteria, are thought to overburden mucosal detoxification systems, causing the colonic epithelial inflammation of ulcerative colitis. However, the possible link between dietary sulfate, colonic hydrogen sulfide levels, and ulcerative colitis has not been adequately evaluated. Special Considerations Kidney failure: Increased blood sulfate levels are a common feature of kidney failure. High serum sulfate levels may play a role in parathyroid stimulation and homocysteinemia, both of which commonly occur in people with chronic kid- ney disease.

OCR for page 397
PART III: SULFATE 401 KEY POINTS FOR SULFATE Sulfate is used in the biosynthesis of many essential 3 compounds, some of which are not absorbed intact when consumed in foods. Inorganic sulfate is needed for the synthesis of 3¢-phosphoadenosine-5¢-phosphosulfate (PAPS), or active sulfate. Neither an EAR, and thus an RDA, nor an AI has been 3 established for sulfate because most people consume adequate sulfate from foods and from sulfate produced in the body. Overall, there were insufficient data to set a UL for sulfate. 3 About 19 percent of total sulfate intake comes from inorganic 3 sulfate in foods and another 17 percent comes from inorganic sulfate in drinking water and beverages. Foods found to be high in inorganic sulfate include dried fruits, certain commercial breads, soya flour, and sausages. Beverages found to be high in sulfate include select juices, beers, wines, and ciders. Sulfate is also present in many other sulfur-containing compounds in foods, providing the remaining approximately 64 percent of total sulfate available for bodily needs. Unlike most other nutrients, the body’s need for sulfate can be 3 met by consuming other required nutrients that contain sulfur amino acids. Thus, a deficiency of sulfate is not found in people who consume normal protein intakes containing adequate sulfur amino acids. Osmotic diarrhea has been reported in people whose drinking 3 water contains high levels of inorganic sulfate. Some association between increased hydrogen sulfide 3 production and the risk of ulcerative colitis has been noted; however, this possible link has not been adequately evaluated.